C. If it cannot be tested would make an idea or theory unscientific. One of the fundamental aspects of science is that ideas and theories must be testable through observation and experimentation. In other words, scientific ideas and theories must be able to be tested to determine whether they are true or false. If an idea or theory cannot be tested in this way, then it cannot be considered scientific. Additionally, it is important to note that an idea or theory does not need to be a fact to be scientific; rather, it must be testable and supported by evidence.